It is known that polyurethane systems employed for producing moldings exhibit strong adhesion to the mold materials that are used, preferably highly thermally conductive materials such as metals. For the production of polyurethane moldings in molds made from the stated materials, there is a need for release agents, which are applied to the mold walls that come into contact with polyurethanes and/or with the polyurethane reaction mixture,
Release agents of this kind are typically composed of dispersions or emulsions of waxes, soaps, oils and/or silicones in solvents such as hydrocarbons. Following application of the release agent to the mold, the solvent evaporates and the nonvolatile substances with release activity form a thin release film which allows the polyurethane molding to be removed easily from the mold following production.
In addition to the release effect that is actually needed, the release agent also takes on further functions. For instance, the release agent also greatly influences the surface of the polyurethane molding, which is to be fine-pored or smooth and uniform, for the purpose, among others, of ensuring that the completed shaped parts can easily be covered with fabrics or leather.
In order to reduce the environmental burden of volatile organic material there is a great interest in release agents which are free from volatile organic material.
One option that is available is to switch to water as the solvent or vehicle for the substances with release activity. However, as compared with conventional release agents containing organic solvents, aqueous release agents that are presently on the market exhibit the disadvantage that, after a major portion of the water has evaporated, there remains a thin film of water left in the mold, which is not volatilized at the typical molding temperatures of 45 to 80° C., preferably 50 to 75° C., and which enters into reactions with the isocyanate compounds of the polyurethane system that lead to very hard polyurea compounds. These compounds form a so-called buildup on the mold surface, which is detrimental to the release effect and must be removed, in a costly and inconvenient operation.
Typical examples of aqueous release agents having a relatively good demolding effect are described, for example, in DE-A-37 42 370 or DE-C-40 20 036. The substance with release activity that these agents contain comprises unsaturated oligomeric or polymeric hydrocarbons having molecular weights of at least 500 g/mol and iodine numbers of at least 60, more preferably the unsaturated oligomeric or polymeric hydrocarbon is liquid polybutadiene having molecular weights of approximately 3000 g/mol and iodine numbers of approximately 450.
A particularly disadvantageous phenomena associated with these release agents are the severe discolorations which occur, and which are caused by oxidation of the double bonds within the unsaturated oligomeric or polymeric hydrocarbons.
A further problem of the above-mentioned release agents is the frequent incidence of allergies among employees who work with these release agents or with the shaped parts produced with their assistance.
In addition to the above-described problem of polyurea buildup on the mold surfaces, these release agents exhibit a further disadvantage that the substance with release activity, which takes the form of a viscous oil, greatly soils the working environment. On machines and equipment, a sticky, greasy film is formed which is difficult to remove; even when great care is taken, the soiling of the surrounding area cannot be avoided with certainty, with the consequence that a slippery, greasy film that is hard to remove is formed, for example, on the floors, and represents an unacceptable hazard potential for the employees.
Owing to the double bonds present in the unsaturated oligomeric or polymeric hydrocarbons, this greasy film can also react further, to form resinous, sticky coats, for example, which are almost impossible to remove with conventional cleaning products.
U.S. Pat. No. 5,218,024, which takes another path, solventlessly uses liquid polymeric polyenes such as polybutadienes having viscosities of approximately 3000 mPa s at 20° C. In some cases, the liquid polymeric polyenes are admixed with additives such as greases, waxes or oils for the purpose of modifying the viscosity and/or enhancing the release effect, and also with further additives such as antioxidants, for instance. Where appropriate, these release agents are sprayed hot.
These release agents, however, are based on the same substances as in D)E-A-37 42 370 or DE-C-40 20 036, which were discussed above, and hence give rise to the same disadvantages, such as strong discolorations and severe soiling of the working environment, through to the buildup of resinous, sticky coats.
In the view of the above, there is a need for mold release agents which are free from volatile organic solvents or water Such mold release agents should not have the abovementioned disadvantages, and more particularly should exhibit a good release effect, or preferably have a beneficial effect on the surfaces of the polyurethane moldings, thus leaving them fine-pored, uniform, and smooth. Additionally, such mold release agents should not leave any buildup of polyurea on the mold surfaces, or contaminate the working environment with a greasy film, yet they should have a low allergy potential.